The use of N-acyl-N-alkylcarboxylates as surfactants is well known. The combination of amido and carboxylate functional groups, coupled with the ability to incorporate a broad range of alkyl substituents, provides a highly desirable range of surfactant properties. Of this class of compounds, the sarcosinates have the widest commercial application. Unfortunately, the synthesis of N-acyl-N-alkylcarboxylates in general, and of sarcosinates in specific, presents a relatively costly approach to address the needs of the surfactant community.
N-acyl-N-alkylcarboxylates have historically been synthesized by reacting the sodium salt of an N-substituted amino acid with a fatty acid chloride in the presence of a strong base. The common industrial method of producing these fatty acid chlorides includes the use of phosphorus trichloride. Fatty acid chlorides produced this way tend to retain trace levels of inorganic or organic phosphorus compounds. These trace impurities often are retained through subsequent steps and lead to undesirable murkiness or cloudiness in the final product.
To further complicate matters, N-substituted amino acids are not common naturally occurring amino acids, and must themselves be produced using rather severe conditions. For example, sarcosine, also known as methyl glycine, is produced by reacting hydrogen cyanide with formaldehyde to form a glycolic nitrile. This nitrile is then condensed with methylamine forming methylaminonitrile. The methylaminonitrile is then hydrolyzed with strong alkali to the sarcosine salt. These relatively costly and undesirable syntheses lessen the commercial attractiveness of sarcosinates for broad use.
The object of the present invention is to provide an alternative route to the commercially valuable N-acyl-N-alkylcarboxylate class of compounds. The invention's reaction sequences eliminate the use of N-substituted amino acids and acid chlorides. Hazardous chemicals typically employed in, for example, the synthesis of sarcosine, such as formaldehyde, hydrogen cyanide, and all nitrile intermediates, are thus avoided. Removing acid chlorides from the synthetic scheme also has the benefit of removing a source of troublesome inorganic and organic phosphorous impurities from the final product. The present invention provides a direct, cost effective alternative to N-acyl-N-alkylcarboxylate synthesis.